Depth-of-field is one of the most important factors in taking a successful picture, even a professional photographer may fail in producing a successful picture if the depth-of-field is poorly managed.
In general, the smaller the aperture is, the longer the depth-of-field gets and vice versa. However, the incoming light is reduced under small aperture and it becomes difficult for the photographer to observe the image of object through viewfinder. Therefore, on most single reflex cameras, the scene is displayed with the maximum aperture for focusing and framing purpose and the aperture is brought down when the release button is pressed to open the shutter for exposure. With this arrangement, the depth-of-field viewed by the photographer through the viewfinder is not the same as that on the actual picture and the photographer has to estimate the depth-of-field and adjust the aperture properly before pressing down the release button.
The common methods for determining the depth-of-field are described as follows:
1. Estimate the depth-of-field by using the depth-of-field scale the lens:
The photographer can use a depth-of-field scale that corresponds to each aperture value on the lens to estimate the possible depth-of-field for every different aperture value. However, it is inconvenient since the photographer has to shift his or her eyesight back and forth between the viewfinder and the scale ring when changing the aperture value. Besides, the precision of the depth-of-field scale is usually poor which can cause errors in reading the scale. Furthermore, this method can only provide a photographer with a rough estimation of the depth-of-field and the information regarding the true vagueness of background and foreground that is related to the actual depth-of-field is not available to the photographer.
2. Check the depth-of-field by using depth-of-field preview button of camera:
The photographer can push down the depth-of-field preview button on the camera to reduce the aperture and check the depth-of-field through the viewfinder. However, since the aperture is reduced after the preview button is pushed, the picture in the viewfinder is darkened and it becomes difficult for the phtographer to determine the depth-of-field and the vagueness of background and foreground.
Due to the many drawbacks in these methods, it is therefore difficult to determine the proper depth-of-field which in turn can cause failures in photographing even for a professional photographer.
There are a great many cameras available in the current market that come with autofocus and autoexposure functions controlled by more advanced software. With these advancements, cameras today can be almost fully automatic. And the current invention is a unique method developed based on these advancements.
Yoshihito Harada has revealed an autofocus camera in the U.S. Pat. No. 5,038,164. The technical merit of this patent is in solving the problem of focusing on two objects in different distances when both objects are to be photographed at the same time. It demonstrates how to use the positions of the two objects of interest, the relationship between in-focus and out-of-focus values, and the position of the lens to determine the aperture value and thus sharply focus on both objects.
Although the '164 has shown that it is capable of finding the aperture value based on the required depth-of-field, it does not provide the photographer with the ability to directly view the area in focus and the vagueness of the background and foreground. It still relies on the commonly used traditional method to estimate the depth-of-field. It has only solved the problem of multi-point focusing and the difficulty encountered by a photographer in determining depth-of-field when composing the layout remains unsolved.